First Report of Fusarium commune Causing Stalk Rot on Maize in Liaoning Province, China

Abstract

Fusarium species are associated with stalk rot disease of maize, which can result in significant yield losses. The typical symptom of the disease is rotting of the plant stem at lower internodes. The color of the plant changes to grayish-green, which later turns tan, and the plant wilts. When the stem is split, the inside of the stalk shows a light pink to tan discoloration and the pith is disintegrated, but the vascular bundles remain intact. During the 2016 crop season, symptomatic maize tissues were collected from four different locations in Dandong city, Liaoning province, China. The disease was found to occur on approximately 5% of the surveyed area. Plant tissues exhibiting typical stalk rot symptoms were cut into small pieces (approximately 5 mm²), placed onto potato dextrose agar (PDA) amended with streptomycin sulfate (150 μg/ml) and kanamycin (150 μg/ml), and incubated at 25°C in darkness for 4 days, as described by Shan et al. (2017). Fungal colonies showing morphological characteristics of Fusarium spp. were subcultured from single conidia onto PDA and carnation leaf agar (CLA) plates for identification and DNA sequence analyses. Microscopic and DNA analyses confirmed the presence of many Fusarium species known to cause ear and stalk rot diseases in maize, such as F. verticillioides, F. graminearum, and F. proliferatum. However, F. commune, a relatively new species described by Skovgaard et al. (2003), was also identified in 12 diseased samples collected from various locations in Dandong city. On PDA plates, colonies of F. commune were white to orange-white in color with densely flocculate to fluffy aerial mycelium and dark violet pigmentation. On CLA plates, macroconidia were slightly curved, hyaline, usually contained three or five septa, with an obvious foot-shaped basal cell and tapering gradually to a point at the tip. Three-septate macroconidia were 39.4 ± 6.2 × 3.7 ± 0.6 μm, whereas five-septate macroconidia were 48.6 ± 4.5 × 4.3 ± 0.3 μm. Microconidia were generally cylindrical, straight to slightly curved, aseptate, and measuring 11.5 ± 3.1 × 3.1 ± 0.7 μm in size. Spherical chlamydospores were 8.6 ± 1.4 × 8.4 ± 1.4 µm in size and were produced singly or in pairs from mycelium. Species identification was also confirmed by partial sequences of the translation elongation factor gene (TEF1-α, EF1 and EF2 primers), the mitochondrial small subunit gene (mtSSU, NMS1 and NMS2 primers), and the second largest subunit of the RNA polymerase gene (RPB2, 5f2 and 7cr primers) (O’Donnell et al. 2010). Partial sequences of the TEF1-α, mtSSU, and RBP2 showed 100, 100, and 99% sequence identity to those of F. commune (GenBank accession nos. KX500397, KY439901, and KU171700, respectively). DNA sequences of partial TEF1-α, mtSSU, and RBP2 from two different isolates were deposited in GenBank (accession nos. MH716808 to MH716813). Pathogenicity tests of two representative isolates were carried out by individually inoculating five maize plants at the five-leaf stage. Maize stalks, at second or third internode, were injected with 20 μl of spore suspension having concentration of 1 × 10⁶ spores/ml as described by Zhang et al. (2016). Five plants inoculated with sterilized water were used as a control. The inoculated plants were maintained at 25 ± 0.5°C in a greenhouse with a 12-h photoperiod. After 10 days, all inoculated plants developed internal dark brown necrotic regions around the inoculated site. The control plants were symptomless. F. commune was reisolated from the symptomatic plants but not from the control. In China, F. commune was also reported to cause root rot diseases in different plant species, for example, sugarcane (Wang et al. 2018) and Gentiana scabra (Guan et al. 2016). To our knowledge, this is the first report of F. commune as a pathogen on maize in China.